The present invention relates to plastic compositions containing a poly (phenylene oxide) polymer (herein sometimes referred to as PPO). More specifically, the present invention covers plastic compositions containing a three component system which consists of PPO, certain bis-phenoxy compounds (hereinafter defined) as flame retardants for said plastic compositions, and an exhancing agent (hereinafter defined) for said flame retardants.
PPO plastics and utility thereof are known in the art as exemplified by Encyclopedia of Polymer Science and Technology, Volume 10, pages 92-111, John Wiley & Sons, Inc., New York, 1969, and which publication is in toto incorporated herein by reference.
The need for flame retarding PPO plastics has also been recognized in the art as exemplified by Encyclopedia of Polymer Science and Technology, ibid, pages 100 and 103, and by U.S. Pat. No. 3,403,036.
The prior art has specifically recognized the problems of finding suitable flame retardants for PPO polymers in view of the fact that polymer systems differ substantially in both flammability characteristics and physical properties and there is no predictability whatsoever from one system to another. Thus in the Norris et al paper entitled "Toxicological and Environmental Factors Involved in the Selection of Decabromodiphenyl Oxide as a Fire Retardant Chemical", Applied Polymer Symposium No. 22, 195-219 (1973), the authors state: "A growing recognition of the huge annual toll taken by fire is resulting in more stringent flammability requirements for synthetic polymers in a variety of applications. Because of economic constraints and the need to produce flame resistant polymers without total replacement of existing manufacturing processes, increased flame resistance is generally achieved by incorporation of a fire retardant chemical in the finished product. This chemical is usually based on bromine, chlorine, phosphorus, or nitrogen and may either be chemically reacted or physically blended into the product. Since polymer systems differ markedly in both flammability characteristics and physical properties, selection of a suitable flame retardant depends on a variety of factors that severely limits the number of acceptable materials.
"A general class of synthetic polymers that require flame retardancy because of their use in electrical and high temperature applications, but pose severe problems in selecting a suitable flame retardant are the high performance thermoplastic resins such as thermoplastic polyesters, polyphenylene oxides, and acrylonitrile-butadiene-styrene (ABS) terpolymers. Some of the most important criteria for an acceptable flame retardant in these applications are:
1. It must be as effective as possible to minimize both cost and effect on polymer properties. Use levels may range up to 15% by weight.
2. It must have sufficient stability to withstand conditions encountered during polymer processing and use. Processing conditions (blending, extrusion, and molding) often involve temperatures exceeding 300.degree. C. The flame retardant must tolerate these conditions without degradation or volatilization. Also, attention must be given to hydrolytic stability and oxidative degradation, particularly under extended service at high temperatures.
3. It must be compatible with the base polymer and exert minimal adverse effect on those properties that give the polymer its value. Some of these critical properties are tensile strength, impact strength, heat deflection temperature, shear strength, and flexural modulus.
4. Finally, the flame retardant must not interfere with attainment of desired product esthetics and form.
"Because of the stringent thermal stability requirements, only a very few compounds have been identified which can meet the necessary performance and economic criteria."
The resultant disadvantages in the utilization of various prior art materials as flame retardants, in general, for plastic compositions include, without limitation, factors such as thermal migration, heat instability, light instability, non-biodegradable, toxicity, discoloration, the large amounts employed in order to be effective, and the unpredictable end results obtained when using the same material in different plastics (note, for example, in Modern Plastics Encyclopedia, ibid, page 650, wherein octabromobiphenyl is suitable for use in polyolefins as a flame retardant therefor, but is not shown for use (or functionally equivalent) as such for the other 27 compositions listed such as ABS; polycarbonates, polystyrene, acrylics and polyurethanes). Thus, it can be seen that the field of flame retardancy is highly sophisticated and consequently requires substantial research effort to achieve a particular desired end result.
In conjunction with the rendition of PPO plastics flame retardant the aforegoing discussion is particularly applicable. Furthermore, it is important that, in addition to the retention of good physical characterstics, three characteristics (one of which is critical) of the product (PPO) be within certain limitations in order to provide a functional flame retarded product. These three characteristics are (1) light stability (as measured, for example, by .DELTA. E color values, hereinafter defined), (2) flame retardancy (as measured, for example, by UL-94, hereinafter defined, and which is a critical characteristic and limitation), (3) thermal stability (as measured, for example, by certain ASTM tests for decomposition and migration, hereinafter defined). This characteristic of flame retardancy is not an arbitrary item but is a criteria which is strictly adhered to in the poly(phenylene oxide) art and hereinafter explained in more detail, with particular reference to the examples contained herein.
In conjunction with the foregoing discussion, the prior art in general suggests the use of halogen-containing materials as "potential" or "possible" flame retardants for plastic materials. However, the prior art also recognizes that any material must be adjudged or a case by case basis because of the unpredictable results of the end product when any additive is incorporated therein. For example, with reference to the use of a halogenated fire retardant in U.S. Pat. No. 3,658,634, attention is directed to the fact that the patentee specifically points out the disadvantages in the use of a halogen-containing fire retardant. In Column 1, lines 14-17, the patentee states: "Therefore, if it is possible to impart fire-retardancy to the thermoplastic polymers without deteriorating the useful properties of the thermoplastic polymers, they can be widely used in the field of inertia, construction and electric industries." In Column 1, lines 26-32, the patentee states: "--the compounds containing chlorine or bromine atoms to be used as fire-retardant agents, are generally sublimated and therefore, the fire retardant agents are sublimated and lost in the process for producing fire-retardant polymers or in after-finishing processes; accordingly, deteriorations of fire-retardancy or difficulties in use tend to occur more often than not."
In Column 1, lines 39-44 the patentee states: "--the compounds containing chlorine or bromine atoms to be used as fire-retardant agents are unstable in most cases when exposed to ultraviolet rays." In Column 1, lines 59-64 the patentee states: "However, as a matter of fact, only very few fire-retardant polymers can be used in actual practice although they are said to have fire-retardant effects, because there are restrictions such as the conditions employed in production attributable to the properties of the fire-retardant agent, or to the properties of the polymers into which they are to be incorporated."
It can be seen, then, from the foregoing discussion and quoted subject matter that the field of flame retardancy is highly sophisticated, unpredictable and requires substantial research to produce an end product (plastic composition) which meets the necessary criteria for utilization purposes, particularly under the present day government standards. Thus, there is always a demand for a material which will function as a flame retardant in PPO polymers and concurrently will not, by incorporation therein, adversely effect the chemical and/or physical and/or mechanical properties of the resultant PPO containing plastic composition (herein also referred to as "PPO plastic composition") and also have utility.
The prior art problem of providing a flame retarded PPO polymer composition having desired chemical, physical and mechanical properties, in addition to functional utility, has now been substantially solved by the present invention and the above-described disadvantages substantially overcome.
Accordingly, one of the main objects of the present invention is to provide PPO plastic compositions which are flame retarded.
Another object of the present invention is to provide a unique three component system for PPO plastic compositions which will not substantially adversely affect the chemical and/or physical and/or mechanical properties of said compositions.
A salient object of the present invention is to provide a PPO plastic composition which has certain defined flame retardancy property.
A further object of the present invention is to provide a flame retardant and an enhancing agent which are economical and easy to incorporate into PPO plastics without being degraded or decomposed as a result of normal blending or processing operations.